Dirt Late Model Project Car

Circle Track Takes On A New Dirt LM Project

For some time now, we have wanted to have a Dirt Late Model project car, but the right situation hasn’t come along-until now. We have a team in Dream Team Motorsports that is very typical compared to probably 90 percent of the teams in the US who run this division. This team is fairly low budget, it loves to race on dirt, and is struggling to redesign and set up its car. It desperately wants success in whatever form it may take, just like most of you.

So, we have taken on the task of helping Bobby Clark with his program this season. We will be evaluating, redesigning, and setting up the car for races at East Bay and Ocala as well as the regional United Dirt Late Model Challenge Series, a 15 race touring series visiting nine tracks in three states-Florida, Alabama, and Georgia. The car was originally a 2002 CJ Rayburn swing arm car that had been modified to a four-bar car. We intend to again modify a recent conversion back to a swing arm car that more closely resembles the original Rayburn design, but not exactly.

This is a year long project and we will be reporting on our work on the car, as well as the results of testing and racing. We have no unrealistic expectations, just a desire to put together a program that will be consistent and that is well thought out. If you can learn something from all of this, then we will have done our jobs.

The evaluation process will involve a review of the entire chassis for structural integrity, safety, design, and setup possibilities. Late in the season last year, the car was involved in a crash and contacted the wall hard on the driver’s side. Several parts of the chassis were bent and these will be removed and replaced.

We will also be looking at previous work done on the car to determine if the welds and other connections are of a suitable quality. We do know that the rear suspension was altered before Bobby owned the car and made into a four-bar suspension. He wants to change the car back to a swing arm suspension and in doing that, we can design some extra adjustment parameters into our new rear suspension.

As we preach constantly, we are doing an evaluation of the moment center location, the rearend alignment, rear steer, front Ackermann effect, weight distribution, and rear traction control devices. We will use many of the important items previously presented in the pages of Circle Track as the basis for the evaluation of this car in order to improve the performance of the total package.

We will be installing new design components from many manufacturers for evaluation. Bobby is in the process of installing new body panels, we are having the engine gone over and refreshed, and we are installing a new drivetrain and rearend along with new wheels and other components.

The nice thing about this car is that in its present condition, it is far removed from a production Rayburn, or any other manufacturer for that matter, and this gives us freedom to do what we want with no disrespect to any car builder. Even the builders can look at what we are doing and make notes. We’re not saying everyone will agree with all we do, but they will know exactly why we are doing it and then let the chips fall where they may.

Our overall design goal is to build a car that is correct for front suspension geometry, and that will be adjustable in a certain range in order to provide a more balanced setup. The new front geometry design will help make the car turn well through the middle, and the balance will make the car both fast and consistent.

We measured the front end already and made a few changes. Take note that what we did might and might not work with your car, even if it is a Rayburn car, due to the fact that we could not determine if the spindles or control arms were the same as the ones that came on the original car. So, we are not saying this chassis is as CJ would have released it new. We are just taking what we have and modifying it to work.

Our goals for setup are to provide a more balanced car on tight tracks where the level of traction is high, and also one that would provide more bite on the drier surface tracks. Along with the spring layout and roll center locations, we are going to design less rear steer into this car and a little different weight distribution than many racers are used to.

In effect, this will be a CT/Bobby Clark car that will showcase critical design parameters and be used to develop a plan of attack for developing and modifying setups for changing track conditions. The overall goal is to use this car as a teaching aid. We will learn from the experience and we hope our readers will learn through our successes and failures as we go along.

Right now, with the initial evaluation completed, we see the following areas of concern and have noted where we will do some redesign. Some of the evaluation will have to wait for installation of the motor, the new rearend, and front end components. Once we have everything installed, we can weigh the car, measure rear steer characteristics, design and install ballast, and work out the spring setups. Here is a short list of items of concern:

1. The front moment center was not where we wanted it, nor even close to where we knew it should be. A quick measure session and entry of the data into a computer program told us that the static MC was at 0.416 inch high and 25.511 inches to the right of centerline, and at mid-turn attitude it went to 1.635 underground and 44.012 inches to the right of centerline.

This is obviously not what we want. So, with the relocation of the upper mounts, the lowering of the lower ball joints to reduce the lower arm angles, the raising of the front ride height by one inch and the changing of the upper arm lengths, we ended up with a static MC location of 2.351 high and 18.945 inches left of centerline, moving to 3.466 high and 2.531 inches left of centerline after dive and roll. This is where the MC in most Dirt Late Model cars needs to be.

I want to stray from our plan of telling you exactly what changes we made in this case because no two chassis are alike, and for you to make the same changes to your car most likely won’t yield the same results. If you want your moment center to be where ours is, measure your car and do the analysis like we did. We ask you to try to learn from the process and not copy the details.

We will also do an Ackermann evaluation at the front to make sure we aren’t gaining too much toe as the wheels are steered, and the steering angles must be equal for both front wheels when steering left or right for dirt.

2. The rearend locating design was a combination of pull bar, double shocks, and a “lift” arm with deceleration control only. We will think about this system and tweak it somewhat using a newer style pull bar and possibly removing the mostly unused lift arm.

3. Rayburn cars of this era used a Z-link system at the rear to locate the ends of the rearend. These systems are usually known for minimal rear steer and a motion ratio for the installed spring rate due to the springs being mounted on the forward links. In our case, the links were mounted at severe angles which would produce quite a bit of rear steer. We will remount these links and provide adjustment to the angles, more so than the original car had.

4. Weight distribution in this car was typical of what we see and read in literature published by some manufacturers. The car had about 58 percent rear weight distribution and 55 percent left-side weight with the driver and all gear aboard. There were no provisions to move weight around easily either.

The desired goal for weight distribution is to be able to move weight from the left to the right in the car and up and down. When running on a tacky surface, we would want more weight on the left side and lower in the car. For dry slick conditions, we would move weight to the right and higher in the car.

Initially, we had to move some weight to the front to get a better front-to-rear percent, to around 52-53 percent rear, so we moved a 30 pound piece of lead from the back of the car to a point at mid-chassis and at around shoulder height next to the driver. This piece came from the rear bumper and should not have been located there for reasons of negative polar moment tendencies. We will talk more about that later.

5. Safety is a concern in any racecar, and we are doing an evaluation of this car along those lines. Bobby had a hard crash last season where he contacted the outside wall hitting on the driver’s side. We are installing a better seat (his bent severely in the crash) and moving it farther to the right. We will install racing-quality padding on the roll bars, around the steering column, and beside his legs. He has also just purchased a new racing-approved Simpson helmet.

An up-to-date fire suppression system will be a part of our safety package too, along with making sure Bobby has properly dated approved seat belts, a sufficiently effective firesuit with racing shoes, and gloves.

As we go along, we will be reporting on our progress and providing details on what we do to the car and why. We will give you exact setup parameters as well as any decisions we make as to setup changes for track conditions. This will not be a generalized reporting, but rather one that tells all. Again, these setups and designs might not work for your car, but the directions we go will demonstrate how successful teams think and act.

We don’t expect to always be right in our decisions. We will tell you when we do something that is not in the right direction. We all learn as much from our mistakes as we do from our successes. A change that does not produce the desired results still teaches us something.

From historical feedback over the past ten years, we have heard that the swing-arm cars, either Dirt Late Models or Dirt Modifieds, are usually very good on the tight and heavy tracks, but do not work as well on the dry slick tracks. We are going to see if we can design this car to work well under both conditions. Only after testing and racing will we really know if that is possible.

We will experiment with different components and spring combinations to try to compensate for changing conditions as we race at different tracks. We will develop a definitive plan of attack to meet the challenge of going from a wet and tacky track to one that is either sandy-dry slick or black-dry slick. We’re going to tell you exactly what that plan is and why we are following it. Any changes we make to the plan will be documented and presented.

Along the way, we want your input, too. As we move through this project, please send along any comments and/or suggestions to us here at Circle Track. By the next issue, we should have the car all ready to race. We can’t wait.

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